In a multi-antenna wireless communications system, a base station generally uses a precoding matrix to transmit data. However, because a channel changes in real time or there is an error in channel information obtained by the base station, a mismatch between a precoding matrix and an actual transmission channel is caused. Signal quality of data that is transmitted according to the precoding matrix and that is received by a user is relatively low. As a result, performance of the wireless communications system is not high.
For example, a precoding matrix is computed according to a direction of arrival (English: Direction Of Arrival, DOA for short) of a terminal that is estimated by a base station. When a spacing between multiple antennas configured for the base station does not satisfy a DOA estimation requirement or coupling happens between multiple antennas, there is an error in the DOA of the terminal that is estimated by the base station. For example, at 2.6 GHz gigahertz, a maximum error in a DOA of a terminal that is estimated by a base station configured with four antennas may be up to 12 degrees. This leads to an error in a precoding matrix computed according to this DOA. In addition, when a relatively large quantity of antennas are configured for a base station, a width of a 3-dB beam formed according to a precoding matrix by the base station becomes quite small. For example, a width of a 3-dB beam formed according to a precoding matrix by a base station configured with 64 antennas is only about 1.5 degrees. Therefore, when a relatively large quantity of antennas are configured for a base station, there is an error in a precoding matrix computed by the base station according to an estimated DOA of a terminal, and a main lobe of a 3-dB beam formed according to the precoding matrix is quite narrow. That is, the 3-dB beam formed according to the precoding matrix by the base station may fail to cover the terminal. Consequently, signal quality of data received by the terminal is relatively low, leading to low performance of a wireless communications system.
Therefore, how performance of a wireless communications system is improved is an urgent problem to be resolved by persons in the art.